Patent application title: STORAGE CONTAINER
Heinz Posselt (Bad Aibling, DE)
IPC8 Class: AF24J204FI
Class name: Solar heat collector with means to convey fluent medium through collector with storage tank for fluent medium
Publication date: 2012-06-21
Patent application number: 20120152234
The invention relates to a storage container (S) for storing a liquid
with a storage space (SP) that is limited toward the bottom by a base (B)
that is flat at least in places and an immersion pump (P) that is
arranged in the storage space (SP), via which the stored liquid can be
removed from the storage container (S). The base (B) of the storage space
has a recess (V) in which the immersion pump is arranged and/or into
which an intake pipe that is connected to the immersion pump extends.
1. A storage container for storing a liquid comprising: a storage space
defined at its bottom by a base that is flat at least in part, and an
immersion pump arranged within said storage space, via which stored
liquid can be removed from said storage container, said base having a
recess in which (a) said immersion pump is arranged, and/or (b) an intake
pipe connected to said immersion pump extends.
2. The storage container according to claim 1, wherein the intake opening of said immersion pump and/or the end of said intake pipe located upstream of the immersion pump lies completely within said recess.
3. The storage container according to claim 1, further comprising a movable separating element, with which the storage space can be separated into an upper partial space and a lower partial space.
4. The storage container according to claim 2, further comprising a movable separating element, with which the storage space can be separated into an upper partial space and a lower partial space.
5. The storage container according to claim 1, further comprising a salt melt is contained within said storage space.
6. A liquid storage system comprising: a first storage container and a second storage container, said storage containers being separate from one another and thermally insulated against the environment, a first set of pump and conduits for removing a liquid from the storage space of said first storage, delivering the liquid to a first heat exchanger coupled to solar absorber, removing the liquid from said heat exchanger, and delivering the liquid to the storage space of said second storage container, and a second set of pump and conduits for removing liquid from the storage space of said second storage container, delivering the liquid to a second heat exchanger coupled coupled to a steam circuit of a steam turbine to produce water vapor, removing the liquid from said second heat exchanger, and delivering the liquid to the storage space of said first storage container, wherein at least one of said first and second storage containers is a storage container according to claim 1.
SUMMARY OF THE INVENTION
 The invention relates to a storage container for storing a liquid having a storage space that is delimited at its bottom by a base that is flat, at least in places, and an immersion pump that is arranged in the storage space, via which the stored liquid can be removed from the storage container.
 Storage containers of the generic type are used in solar thermal power plants for intermediate storage of solar energy. Solar thermal power plants use solar energy to generate electric current. With a mirror, the solar radiation is focused on an absorber and converted into heat, which is transferred to a thermo-oil that circulates in a closed circuit. The thermo-oil, which is heated in the absorber to a temperature of approximately 400° C., releases part of its heat energy via a heat exchanger, whereby superheated water vapor is produced. Cooled in the heat exchanger to a temperature of approximately 300° C., the thermo-oil ultimately goes back to the absorber. The superheated water vapor is expanded in a steam turbine that is coupled to a generator, and electric current is produced in this way. In order to be able to produce electric current in periods in which the sun does not appear, a solar thermal power plant usually comprises a thermal salt-melt reservoir, in which a part of the solar heat absorbed via the absorber is stored during sunny periods and from which heat is removed for power production during periods of little or no sun.
 According to the state of the art, such a heat reservoir has two storage containers that are separate from one another and that are thermally insulated against the environment, between which a salt melt that is used as a coolant can be pumped back and forth. For heat storage, salt melt is removed from the storage space of a first storage container at a temperature of approximately 300° C., heated to approximately 400° C. via a heat exchanger that is coupled to the absorber, and then pumped for intermediate storage into the storage space of a second storage container. For example, at night, salt melt is removed from the second storage container, cooled to approximately 300° C. via a heat exchanger coupled to the steam circuit of the steam turbine under production of water vapor, and then recycled into the storage space of the first storage container. One type of dual storage tank system for use with solar power plants is described in US 2011/0168159, hereby incorporated by reference.
 The storage containers of thermal salt-melt reservoirs typically have a cylindrical storage space with a diameter of approximately 37 m and a height of approximately 14 m, by which they can accommodate up to 28,000 tons of salt melt. For removal of salt melt, an immersion pump is arranged in the storage space in such a way that its intake opening is located above the flat storage space base. To ensure, i.a., that the immersion pump does not suck in any air during the operation of the thermal salt-melt reservoir, the level of the salt melt is reduced only up to a minimum height, which is approximately 1 m. In the two storage containers, there therefore always remains a minimum amount of approximately 4,000 tons of salt melt, which cannot be used for the heat storage, for which, however, investment costs on the order of several million Euro accumulate.
 Thus, an object of the invention is to provide a storage container of the above-mentioned type by which the drawbacks of the state of the art are overcome.
 Upon further study of the specification and appended claims, other objects and advantages of the invention will become apparent.
 These objects are achieved by providing a recess in that the base of the storage space in which the immersion pump is arranged and/or into which an intake pipe that is connected to the immersion pump extends.
 The recess is configured in such a way that when stored liquid is removed, the liquid can flow with negligible pressure loss into the intake opening of the immersion pump or the end of the immersion pipe located upstream from the intake opening.
 Preferably, the intake opening of the immersion pump and/or the end of the intake pipe located upstream are found completely within the recess. They are especially preferably arranged so deep that the stored liquid can be removed at least up to the free volume of the recess without there being a risk of air being aspirated by the immersion pump. In this case, the free volume of the space content of the recess is defined minus the volumes of internal components arranged in the recess, such as, for example, the immersion pump.
 The storage container according to the invention can be designed with an undivided storage space. A variant of the invention, however, calls for the storage container to be of a type as disclosed in a patent application filed with the German Patent and Trademark Office under number 102010034294.7 (hereby incorporated by reference) and which therefore has a movable separating element with which the storage space can be separated into an upper partial space and a lower partial space.
 All of the liquid stored in the storage space can be removed from the storage container according to the invention, except for a remainder that corresponds to approximately the filling amount of the recess. In particular, when the storage container is used in the thermal salt-melt reservoir of a solar thermal power plant, considerable financial advantages are produced relative to the state of the art, since the same amount of heat can be stored with a considerably smaller amount of salt melt.
BRIEF DESCRIPTION OF THE DRAWINGS
 The invention is illustrated schematically with reference to an exemplary embodiment in the drawing and will be described extensively hereinafter with reference to the drawing. Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing wherein:
 FIG. 1 depicts an embodiment of the invention.
 FIG. 1 shows a section through a storage container according to the invention, as it can be used, for example, in the thermal salt-melt reservoir of a solar thermal power plant.
 The storage container S essentially comprises a jacket M that is configured as a vertical cylinder, which is connected to a base plate B in a liquid-tight manner. Jacket M and base plate B are surrounded with a heat-insulating layer 1 and enclose a storage space SP, in which a liquid coolant, such as, e.g., a salt melt, can be stored. This structure stands on a cast-concrete base R. The storage space SP is delimited at its bottom by the base plate B, which forms its base, and is flat up to the recess V. The immersion pump P is arranged in the recess V in such a way that its intake opening is located completely within the recess V. A pipeline 1 runs outward from the immersion pump P, via which the liquid coolant can be fed to a heat exchanger (not shown).
 The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German Application No. DE 10 2010 055450.2, filed Dec. 21, 2010 are incorporated by reference herein.
 The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.
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